Preparation of siloxanes containing carboxy groups



United States Patent PREPARATION OF SILOXANES CONTAINING CARBOXY GROUPS 7 1 Claim. (Cl. 26046.5)

This invention relates to organosilanes and to the siloxanes derived therefrom.

Disiloxanedicarboxylic acids of the formula [HOOC (CH2 nSi (CI-l3 2120 where n has a value from 2 to 5, are disclosed and claimed in U. S. Patent 2,589,446. It is also disclosed in this patent that when these carboxylic acids are heated in the presence of mineral acids, lactones are formed. Due to this lactone formation, it is not possible to copolymerize the above disiloxanes with other types of siloxanes by means of the well known acid copolymerization method which involves the rearrangement of siloxane bonds. Since the above materials are acidic in nature, it is obviously not possible to carry out copolymerization using alkaline materials. Consequently, to date there has been no practical method for forming copolymers of the above carboxylic disiloxanes with other siloxanes such as dimethylsiloxanes. Such copolymers are desirable because it would allow the formation of siloxanes in which the molecules have terminal units bearing carboxyl groups.

It is an object of this invention to provide intermediate compounds for use in preparing organopolysiloxanes having carboxyl groups in the molecule. Another object is to prepare materials which are useful for coating compositions, lubricants and additives for conventional siloxane fluids and resins.

This invention relates to silanes of the formula XOC(CH2)nSi(CI-I3)2X where X is alkoxy or chlorine and n has a value from 2 to 5 inclusive.

The silanes where X is chlorine are prepared by reacting the corresponding disiloxane dicarboxylic acids supra with thionyl chloride. As a result of this reaction, the carboxyl group is converted to an acyl chloride group and the siloxane linkage is cleved to give a chlorosilane.

The silanes in which X is alkoxy are prepared by refluxing the corresponding dicarboxylic acids supra in an acidic alcoholic solution. This causes esterification of both the silicon and the carboxyl group. For the purpose of this invention, any primary monohydric alcohol may be employed in this method. Operative alcohols are, for example, methanol, propanol and octadecanol.

Another method by which the above alkoxy silanes can be prepared is by reacting the corresponding chlorosilanes supra with monohydric alcohols. If desired, a hydrogen halide acceptor such as pyridine may be used in the reaction. In this procedure any monohydric alcohol may be employed such as for example methanol, tertiary butanol and isopropanol.

In accordance with this invention, the above hydrolyzable silanes are cohydrolyzed with silanes of the formula RmSlX4-m, where R is a monovalent hydrocarbon radical free of CEC linkages, m has a value from 0 to 3, and X is chlorine or alkoxy, to give the siloxanes of this invention. This cohydrolysis is carried out in the normal manner for cohydrolyzing silanes. For example, the mixed silanes may be added to a mixture of solvent and Water. Suitable solvents include toluene, ether, and

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dioxane. After hydrolysis is complete, the resulting copolymeric siloxane is washed free of acid. In carrying out the cohydrolysis, it is preferred that the temperature be kept below about 50 C. in order to avoid formation of lactones. Once the cohydrolysis has been completed, the resulting copolymer may then be heated at a higher temperature in order to increase its degree of polymerization.

The siloxanes which are prepared according to the method of this invention are copolymers containing from .001 to 99 mol per cent siloxane units of the formula HOOC(CH2)11,(CH3)2SlO1/2, where n has a value from 2 to 5 inclusive, and from 1 to 99.999 mol per cent siloxane units of the formula R SiO m T where R is a monovalent hydrocarbon radical free of C50 linkages and m is an integer from 0 to 3 inclusive. In the copolymers there is an average of from .9 to 3 of the defined organic radicals per Si atom.

The copolymers of this invention can contain siloxane units of the formulae SiOz, RSiO3 2, R2Si0 or R3SiO1 2. These units may be present in any combination which gives an average of at least .9 organic groups per silicon atom.

The monovalent hydrocarbon-substituted siloxanes within the scope of this invention may have any monovalent hydrocarbon radical attached to the silicon except those radicals which contain acetylenic linkages. Thus,

. the siloxanes may be substituted with alkyl radicals, such Example 1 55.7 g. of the acid sh [HOOCCHzCHzSihO was mixed all at once with 71.4 g. of SOClz. The mixture was warmed at 40 to 45 C. for 4% hours with stirring. Upon distillation of the product, 61.2 g. of

CIOCCHzCHzSiCl boiling at 77 C. to 78 C. at 12 mm. and having a refractive index at 20 C. of 1.4568 was obtained.

Example 2 When the acids shown below are reacted with thionyl chloride in the manner of Example 1, the following chlorosilanes are obtained.

Acid Chlorosilane (CH9: CH 1 [HOOC(CHr)zSl- ,0 OlOC(CH2)@(S3igl;

3 2 2 [HOOG(CHz)4Si- 1,0 ClOC(CH2)4(SJlG l 3 a [HOOC(CHz)5Sl- 1,0 oloownagsioi Example 3 (CH3): [HOOCCHnCHzSihO O: C2Hs0 O C CHz CH2SiOC2H boiling at .92" C. at 2 mm. and having a refractive index at 20 C. of 1.4201.

Example 4 When the acids of Example 2 are treated in accordance with the method of Example 3, the following esters are obtained.

Acid Ester Example 5 When one moi of C1O(CH2)zSi(CH3)2Cl is mixed with mols of dimethyldichlorosilane and the mixture is added slowly to an agitated mixture of 500 g. of ice and one liter of toluene, a fluid cohydrolyzate comprising dimethylsiloxane chains end-blocked with HOOCCH2CH2(CHa)2SiO.5

units is obtained.

Example 6 The following copolymers are obtained when the corresponding chlorosilanes are cohydrolyzed in accordance with the procedure of Example 5.

M01220?- cen 0 Chlorosflane Srioxane total polymer phenylmethylsiloxane- 20 monomethylsiloxane 30 1 CH Si0l3.-.. monophenylsigoifirseu. 30

a z C1OO(CH Si(CH O1 HOOO(CH2)3SiO1 2 20 CmHs'JSlCls monooctadecylsiloxane 5 (C4H9)2 iClz dibutylsiloxane 15 C6H10(CH )zSlC1 cyclohexyldirne'thyl- 5 2 siloxane.

"' C3H3(CH3)S1OI2 vinylmethylsiloxane..- 25 011331013 monomethyls'tloxfialieu 48 a 2 G1OC(CH2)5S1(OH3)BC1 HOOC(CHz)5SiO /z 2 3 {(OGHQ SiCIZ diphenylsiloxzzreilfnn 99. 98

a Cl0O(CH2)4Si(CH3);C1 HOOC(CHz)SiO1/2 .02

That which is claimed is:

A method of preparing copolymeric siloxanes which comprises cohydrolyzing a compound of the formula XOC(CI-I2)nSi(CI-I3)2X, where X is selected from the group consisting of chlorine and alkoxy radicals and n is an integer from 2 to 5 inclusive, with a silane of the formula RmSlX4m, where R is a monovalent hydrocarbon radical free of C50 linkages, and X is selected from the group consisting of chlorine and alkoxy radicals and in has a value from 0 to 3 inclusive, at a temperature below 50 C.

References Cited in the file of this patent UNITED STATES PATENTS 2,486,162 Hyde Oct. 25, 1949 2,500,761 Lewis Mar. 14, 1950 2,589,446 Sommer Mar. 18, 1952 2,589,447 Sommer Mar. 18, 1952 OTHER REFERENCES Sommer et al.: Jour. Am. Chem. $00., vol. 72 (1950) pages 19351939. 

